The present invention relates to an high pressure fuel supplying apparatus for in an internal combustion engine, which apparatus sends high pressure fuel to a fuel injection system of the engine, and to a method for controlling the apparatus.
Japanese Laid-Open Patent Publication No. 10-61468 discloses a high pressure fuel pump having a plunger that is reciprocated by rotation of a crankshaft of an engine. Reciprocation of the plunger in a pressurizing chamber draws fuel into the pressurizing chamber and pressurizes the drawn fuel. The pressurized fuel is sent to a delivery pipe.
During a suction stroke of the plunger, in which the pressurizing chamber is expanded, an electromagnetic valve located in the pressurizing chamber is supplied with no current and is thus opened. As a result, fuel is supplied to the interior of the pressurizing chamber from a feed pump, which forms part of a fuel supply source. During a pressurizing stroke of the plunger, in which the pressurizing chamber is compressed, the electromagnetic valve is supplied with current and closed at a time corresponding to the amount of fuel that is to be sent to the fuel injection system. As a result, fuel in the pressurizing chamber is pressurized. The pressurized fuel pushes open a fuel discharge valve and is supplied to the delivery pipe, which forms part of a fuel injection system.
The plunger of the aforementioned publication is reciprocated by rotation of the crankshaft of the internal combustion engine. Therefore, in order to determine the stroke position of the plunger in the pressurizing chamber, the rotational phase angle of the crankshaft must be identified. However, the rotational phase angle of the crankshaft cannot be identified, for example, when the engine is being cranked. At this time, it is impossible to control the electromagnetic valve according to a normal process even if the high pressure pump is operating. Thus, when the engine is being cranked, high pressure fuel is not supplied to the fuel injection system, and fuel in the fuel injection system is not pressurized at an early stage. This hinders a desirable fuel injection and degrades the starting of the engine.
To eliminate this drawback, the technology disclosed in the above publication pressurizes fuel in the fuel injection system at an early stage in the following manner. That is, when the rotation phase angle of the crankshaft is not identified, a duty control is performed to supply and stop current to the electromagnetic valve in short cycles. Each suction stroke of the plunger corresponds to each current stopping period of the duty control. In each current stopping period, the electromagnetic valve is opened, and fuel is drawn into the pressurizing chamber. When the plunger is at a pressurizing stroke, the electromagnetic valve is closed at a first current supplying timing in the duty control. During this closing period of the electromagnetic valve, the pressure of the fuel in the pressurizing chamber increases. Although current to the electromagnetic valve is stopped after the closing period, the pressure of the fuel in the pressurizing chamber maintains the closed state of the electromagnetic valve. In the subsequent pressurizing strokes, the electromagnetic valve is not opened regardless of whether the duty control is performed. Therefore, even if the rotational phase angle of the crankshaft is not identified, the pressure of the fuel in the pressurizing chamber is increased, so that the fuel pushes open the fuel discharging valve and is supplied to the fuel injection system in a pressurized state.
However, when the engine is being cranked, the voltage of a power supply, such as a battery, is lowered due to an electrical load created by activation of a starter motor. If the voltage is significantly lowered, the electromagnetic valve is not completely closed during the current supplying period in the duty control, which results in an insufficient pressure increase in the pressurizing chamber. This possibly hinders the fuel injection system from receiving high pressure fuel, and prevents the pressurizing efficiency of fuel supplied to the fuel injection system from being improved.
Accordingly, it is an objective of the present invention to provide a high pressure fuel supplying apparatus for an internal combustion engine and a method for controlling the apparatus, which apparatus and method improve the pressurizing efficiency of fuel supplied to a fuel injection system.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a high pressure fuel supplying apparatus is provided. The apparatus pressurizes fuel supplied from a fuel supply source and sends the pressurized fuel to a fuel injection system of an internal combustion engine. The apparatus includes a fuel pump, an electromagnetic valve, a voltage detecting device, and a controller. The fuel pump has a pressurizing chamber, and repeats a pressurizing stroke and a suction stroke in accordance with rotation of the engine. During each suction stroke, the fuel pump draws fuel from the fuel supply source to the pressurizing chamber. During each pressurizing stroke, the fuel pump pressurizes fuel in the pressurizing chamber and sends the pressurized fuel to the fuel injection system. The electromagnetic valve selectively connects and disconnects the pressurizing chamber with the fuel supply source. The electromagnetic valve is actuated by electricity supplied from a power supply. The voltage detecting device detects a voltage of the power supply. The controller controls the electromagnetic valve. To adjust an amount of fuel to be supplied to the fuel injection system, the controller determines opening and closing timing of the electromagnetic valve based on a rotational phase of the engine. When the rotational phase of the engine is not identified, the controller executes a duty control to cyclically repeats supplying and stopping of current to the electromagnetic valve. The controller extends a current supplying period in each cycle of the duty control as the voltage detected by the voltage detecting device is lowered.
In another aspect of the present invention, a method for controlling a high pressure fuel supplying apparatus for an internal combustion engine is provided. The apparatus includes a fuel pump having a pressurizing chamber and an electromagnetic valve. The fuel pump repeats a pressurizing stroke and a suction stroke in accordance with rotation of the engine. During each suction stroke, the fuel pump draws fuel from a fuel supply source to the pressurizing chamber. During each pressurizing stroke, the fuel pump pressurizes fuel in the pressurizing chamber and sends the pressurized fuel to a fuel injection system of the engine. The electromagnetic valve is actuated by electricity supplied from a power supply to selectively connect and disconnect the pressurizing chamber with the fuel supply source. The method includes: determining opening and closing timing of the electromagnetic valve based on a rotational phase of the engine, thereby adjusting an amount of fuel to be supplied to the fuel injection system; executing a duty control to cyclically repeats supplying and stopping of current to the electromagnetic valve when the rotational phase of the engine is not identified; and extending a current supplying period in each cycle of the duty control as the voltage of the power supply is lowered.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.